A coordinate measuring machine for measuring structures on substrates, which is used for the production of wafers, is described in the lecture script “pattern placement metrology for mask making” by Dr. Carola Bläsing. The lecture was given on the occasion of the Semicon conference, Education Program, in Geneva on Mar. 31, 1998. For details on the operation and structure of the coordinate measuring device, please see the mentioned publication and the commercially available devices (currently IPRO III).
Since the present invention may be used advantageously in a coordinate measuring machine, there is primarily described such a coordinate measuring machine without limiting the generality. In the present application, the terms “samples”, “substrate” and the general term “object” are used as synonyms. In the production of semiconductor chips arranged on wafers, the structure widths of the individual structures are becoming smaller and smaller as the packing density increases. Correspondingly, the requirements for the specification of coordinate measuring machines used as measuring and inspection systems for measuring edges and positions of structures and for measuring the structure widths are increasing.
In addition, the modern masks in the semiconductor industry are very often used with a structured illumination in the stepper so that the structures are imaged on the wafer with this structured illumination. It is very important for the user to know the position and the dimension of a structure on a substrate illuminated with an illumination as it is also used in the stepper for the production. The exact geometry of this illumination ultimately depends on the structures on the mask or the substrate. For example, dipole illumination is very often used for masks on which mainly dense line arrays are to be imaged. This has the advantage that the contrast of the mask image on the wafer is increased as compared to a homogeneously illuminated, rotationally symmetric pupil. The prior art coordinate measuring machines operate with a homogeneously illuminated pupil of fixed size. The pupil size or shape cannot be adjusted. In addition, there is also used unpolarized light.